Current network architectures are configured to allow optimal transmission of binary data in the digital and optical domain. Network users typically require varying degrees of protection for the transmission of the data depending on the applications being used by the particular network user. For example, some users may not need any protection for low priority data applications, and therefore can withstand multiple interruptions for extended periods of time. Other users, however, may be using high priority data applications that require immediate protection of the data traveling over a service optical fiber line.
Protection for data traveling over the service optical fiber line, i.e., service data, may be achieved by alternately routing the service data through unaffected equipment and transmission lines when a hardware fault occurs. After detecting the fault, the existence of the fault is typically communicated to an element management processor or a similar element in a network management system, which executes control algorithms to implement the re-routing of the data. To implement the re-routing of the data, a switch is effected to a protection route. The process of detecting the fault, communicating the existence of the fault and switching to a protection route results in a certain amount of delay between the detection of the fault and the re-routing of the data.
FIG. 1 illustrates a network protection system for a ring architecture of an optical network. As shown in FIG. 1, the network protection system 10 includes a plurality of line terminating equipment (LTE) 12, 14, 16 and 18, service rings 22 and 26, protection rings 24 and 28, and a network management system (NMS) 20. In the example shown in FIG. 1, a fault occurs between LTE 12 and LTE 14 in the form of a fiber cut. As a result of the fiber cut, LTE 14 will see a variety of out of tolerance conditions for data received from LTE 12 over service ring 22, which is communicated to the NMS 20. The NMS 20 implements a switch to the protection ring 24 in the transmission from LTE 12 and in the reception at LTE 14. A similar situation occurs in reverse for the service ring 26 and the protection ring 28.
Between the time that the fault is detected and the switch is made to the protection ring from the service ring, there is a delay time TD. The delay time TD is the sum of the following times: fault detection time TFD; communication time to the NMS 20 TCINMS; decision time by the NMS 20 TNMSD; communication time to the transmitting LTE 12 for switching transmission TC2NMS; switching time at the transmitting LTE 12 TSW1; communication time to the receiving LTE 14 for switching reception TC3NMS; and switching time at the receiving LTE 14 TSW2. When a fault occurs at a time T0, the next data received is the data sent at time T0+TD. As a result, the data transmitted between the time T0 and the time T0+TD is lost.
Among the different times contributing to the delay time TD the fault detection time TFD may be very short, but the time to communicate the fault to the NMS 20, TC1NMS, such as with an emergency flag propagating through control layers of the network protection system 10, can be significant. After receiving the flag, the NMS 20 decides what action to take. Since many other alarms may be received simultaneously, a latency period may occur before any action is taken, which increase the decision time TNMSD by the NMS 20. Once the NMS 20 has determined the response to the fault, the NMS 20 communicates the response to the affected LTEs, which trigger the appropriate switches. Although optical switches have fairly fast response times, resulting in relatively short switch times TSW1 and TSW2, there is typically a significant delay with respect to the times TC2NMS and TC3NMS for the NMS 20 to communicate the switches to the LTEs.
FIG. 2 is a block diagram of a conventional network protection system for a 1+1 configuration of an optical network. As shown in FIG. 2, the optical network includes transmission protocol devices 32, 34 and 44, line terminal equipment (LTE) 36, 38 and 40, a protection switch 42, a service line 46 and a protection line 48. The 1+1 configuration of FIG. 2 provides for the simultaneous and synchronous transmission of data through the service line 46 and the protection line 48.
In the optical network, the same data signals are received by the transmission protocol devices 32 and 34 for the service line 46 and the protection line 48, respectively. The data signals output from the transmission protocol devices 32 and 34 are respectively received by the LTEs 36 and 38. The LTEs 36 and 38 each combine the data signals into a single multiplexed signal (WDM signal) and transmit the WDM signal respectively over the service line 46 and protection line 48. The WDM signal from the service line 46 is received by the LTE 40, which demultiplexes the WDM signal into the respective data signals and outputs the data signals to the transmission protocol device 44. The WDM signal output from the protection line 48 is received by the protection switch 42, which selectively switches the WDM data signal from the protection line 48 to the LTE 40 in response to the detection and processing of a fault in the service line 46.
Like the ring architecture of FIG. 1, there is a delay time TD between the time a fault is detected in the service line and the time the switch in the protection switch 42 is made to provide the WDM data signal from the protection line 48 to the LTE 40. Consequently, the 1+1 configuration shown in FIG. 2 also loses the data that would have been received over the service line 46 during the delay time TD.